Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsAn HPROF file is a point-in-time snapshot of a Java heap. Open it with Eclipse Memory Analyzer Tool (MAT) to investigate retained objects and Java-heap memory leaks; use different evidence for native-memory failures or growth over time. For modern HotSpot JVMs, common ways to collect a dump are -XX:+HeapDumpOnOutOfMemoryError and jcmd.
What an HPROF file can—and cannot—tell you
An HPROF heap dump records objects and their relationships at the moment it was captured. Depending on the dump type, it can also include classes, garbage-collection roots, thread stacks, and local variables. MAT can use those details to show what remains reachable and what is retaining it. Eclipse MAT’s heap dump overview explains the contents and limits.
A dump is not an allocation history: it cannot, by itself, identify who created an object or where that object was allocated. If you need to know what grew over time, compare snapshots or use Java Flight Recorder (JFR) with heap statistics. Oracle documents heap statistics as a way to identify top growers in a recording. Oracle’s memory-leak troubleshooting guide
How to collect a heap dump
Choose a collection method supported by the JVM you are diagnosing. The commands below are documented for HotSpot; check your JVM vendor’s documentation for other implementations.
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Capture automatically when an OutOfMemoryError occurs
Start the JVM with -XX:+HeapDumpOnOutOfMemoryError. Set -XX:HeapDumpPath to a writable location with enough free disk space, for example -XX:HeapDumpPath=/var/tmp/java.hprof. Oracle documents both options in its Java launcher troubleshooting options. Confirm that the process can write to the chosen directory; a dump cannot be saved if the path is inaccessible or the disk is full.
Capture from a running HotSpot JVM
Find the target process ID, then run jcmd <pid> GC.heap_dump filename=heapdump.dmp. Oracle documents the GC.heap_dump diagnostic command in the jcmd reference. Run the command in an environment with access to the target process, and choose a destination with sufficient space.
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Another documented option is jmap -dump:format=b,file=snapshot.jmap <pid>. MAT also describes using JConsole’s HotSpotDiagnostic dumpHeap operation to request a dump. See MAT’s heap dump acquisition guide for collection alternatives.
Do not use the old -agentlib:hprof=heap=dump,format=b method for Java 9 or later: the HPROF agent was removed in Java 9. Prefer the automatic OOM option or jcmd on modern HotSpot. The Java 9 change is documented in the Java 9 migration guide.
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How to investigate a Java-heap memory problem in MAT
Oracle describes heap dumps as important evidence for troubleshooting memory leaks, but a dump is a snapshot, not proof of the historical cause. Use it to determine which objects are retained and why they remain reachable.
- Preserve the original and note the context. Record the JVM vendor and version, startup flags, the failure message, and when the dump was captured. Keep an untouched copy before experimenting with tools.
- Open the file in MAT. Allow parsing to finish. If parsing fails, record the exact error before trying another copy or dump.
- Inspect the overview and class histogram. Look for classes with large object counts or heap use. Sort by retained heap to focus on objects whose removal would release the most memory.
- Follow dominators and paths to GC roots. A dominator tree helps identify objects retaining other objects; paths to garbage-collection roots show why those objects are still reachable. Check whether the retaining reference is expected application state, a cache, a listener, a thread-local, or another long-lived structure rather than assuming that a large class count alone proves a leak.
- Correlate the result with runtime evidence. Compare the retained objects with heap sizing, GC logs, request traffic, and the relevant code path. MAT’s collection analysis guide describes investigation tools.
For repeatable triage, MAT also provides the command-line ParseHeapDump tool for generating histograms or running Object Query Language (OQL) queries. See MAT’s command-line documentation.
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Why MAT may report an invalid or truncated HPROF
An “Invalid HPROF file” error can mean the file ends before all declared record bytes are present. MAT also reports parsing problems for illegal record lengths or types, unsupported segment types, unresolved names, and missing heap-dump indexes. These messages are clues about file integrity or compatibility, not a diagnosis of the Java program’s memory behavior. MAT lists parser errors in its FAQ.
- Check the file itself: verify that the transfer or copy completed and that the destination disk did not run out of space during capture.
- Recapture if needed: if the file is incomplete or corrupt, collect a fresh dump using a supported method and writable destination.
- Check producer and consumer compatibility: confirm the MAT version supports the dump variant produced by the JVM, particularly if the error refers to unsupported records or segments.
When the failure is native memory, not Java heap
A Java-heap HPROF may not explain a native-memory failure. OpenJ9 documents address-space pressure and duplicate class loading among causes of NativeOutOfMemoryError. Its guidance directs users to native-memory sections and MAT’s Class Loader Explorer when investigating duplicate classes. See the OpenJ9 native-memory troubleshooting guide.
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Distinguish the failure from ordinary Java-heap exhaustion before interpreting the dump. Use the JVM-specific native-memory tools and guidance for the implementation in use; a heap snapshot shows Java object reachability, not a complete accounting of native allocations.
Quick Recap
Choose evidence that matches the question
| Question | Useful evidence | What it establishes |
|---|---|---|
| Which objects are retained now, and what keeps them reachable? | HPROF opened in MAT | A point-in-time view of Java-heap objects and reachability; not the objects’ allocation sites. |
| Can I collect a repeatable heap snapshot from HotSpot? | jcmd or, where appropriate, jmap |
A command-line route to a heap dump; support depends on the target JVM. |
| What is consuming native memory? | JVM-specific native-memory tools | Evidence aimed at native memory; a Java-heap HPROF alone is insufficient. |
| Which objects or classes are growing over time? | Multiple snapshots or JFR with heap statistics | Comparative or time-series evidence; a single HPROF has no allocation history. |
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